The present invention disclosed herein relates to a communication apparatus, and more particularly, to a polarization division multiplexed optical Orthogonal Frequency Division Multiplexing (OFDM) transmitter and receiver.
OFDM is a communication system that allocates a wide band signal to a plurality of vertical subcarriers having a narrow interval, and modulates and transmits each of the subcarriers at a relatively low symbol speed. As technology capable of coping with high spectrum efficiency and a multiplexing fading effect, an OFDM communication technology is much used in Worldwide Interoperability for Microwave Access (WiMAX), wireless Local Area Network (LAN), Asymmetric Digital Subscriber Line (ADSL), a digital radio and a video broadcasting system.
Recently, research is actively being made on optical OFDM that applies an optical communication technology to OFDM. An optical OFDM technology is recognized as technology having a large allowable value for a factor that deteriorates the quality of an optical signal like the chromatic dispersion of an optical fiber and polarization mode dispersion. As a method for increasing the transmission speed of an optical signal, a polarization multiplexing technology is being applied. The polarization multiplexing technology is one that multiplexes an optical signal into two polarization components (for example, x-polarization and y-polarization) within a bandwidth for increasing a signal transmission speed, thereby transmitting the multiplexed polarization components. As described above, a case of applying an optical communication technology and a polarization multiplexing technology to OFDM is called polarization division multiplexed optical OFDM.
A polarization division multiplexed optical OFDM technology is one requiring an operation that estimates and synchronizes the characteristics of channels for each polarization. As such a technology, various types of channel estimation methods and synchronization methods have been proposed. However, the currently-proposed channel estimation method and synchronization method of the polarization division multiplexed optical OFDM have characteristic for only a channel estimation function or synchronization. Accordingly, polarization division multiplexed optical OFDM having characteristic for both a channel estimation function and synchronization is required.